Implement SQLite/T-SQL compatible syntax for get_SDA_*() methods

[brownag]

• 1. Why is SQLite GROUP_CONCAT() so slow when run locally?
  • resolved by adding indices to e.g. createSSURGO()

2. Generalize temporary table conversion

• get_SDA_property(): dominant component (numeric), weighted average, min/max aggregation
• get_SDA_interpretation(): dominant component (numeric) and weighted average, min/max aggregation
• get_component_from_SDA()

Further development following #246; I think I have figured out an approach to handle TODO item 2, that with indexing of the temp tables may resolve item 1.

EDIT: indexing of the tables alone resolves item 1, temporary tables are a much more involved fix for many different queries

[brownag]

At long last, in #381, I've developed a scheme for dealing with item 2 (part 1) using CTEs.

This applies to certain aggregation methods in get_SDA_property(), get_SDA_interpretation() as well as get_component_from_SDA().